We’re collaborating with Christina T. Miller Sustainable Jewelry Consulting to bring you a series of blogs, each building on the next, to expand on what we know about gold, how gold is mined, and what issues exist in the way gold is sourced and why. Finally, we’ll get into gold jewelry itself and how it’s made responsibly. Stay tuned each month for a new story.

3.9 billion years ago, gold fell from the sky. 

It was a major meteoric event that happened 200 million years after the earth formed, and it’s why we have access to gold today. Gold “falling from the sky” also starts to answer a question that has been puzzling scientists for a long time: Where does gold come from? 

When Earth was first formed, precious metals (like gold) were pulled and trapped in our planet’s dense core. This core gold is both locked up more securely and more plentiful than the gold bars in Fort Knox. In 2005, Professor Bernard Wood, a geologist, ran the calculations and estimated that you spread core gold like butter over Earth’s entire surface, the layer would be 18 inches deep!

But if all this gold is locked in the Earth’s core, why can we find it in rivers, mountains, and lowlands across the planet?

This is the question that scientists are beginning to understand how to answer.

The prevailing theory as to why there is gold on the crust and in the mantle is that meteorites containing gold, platinum, iron, and other minerals hit Earth after its core was already formed. When impacting the molten surface of the earth, the meteorites melted — and their minerals were caught up in fiery currents. Ultimately, they distributed gold and other minerals throughout the hot, churning surface. 

Figuring this out has not been easy, and scientists have had to use a different mineral entirely to run their tests: tungsten. Tungsten has enabled the differentiation between old rocks (3.9 billion years old) and even older rocks (4 billion years old) that were here when Earth was first formed. As it turns out, some rocks have trace tungsten, and some don’t; those that don’t have had the tungsten (and gold) removed by Earth’s core. The rocks that do have tungsten and gold formed later, after the meteor strike. 

Today, we can find gold all over the world — and the only continent where active mining is not taking place yet is Antarctica. The first half of the story of “Where does gold come from?” went as far back in time as possible, when Earth’s surface was still molten. The majority of meteoric gold is in the earth’s mantle, a layer deeper than where we mine.

So how did we get from Earth’s molten surface to the planet (and gold) we know today? 

Plate tectonics, volcanic activity, erosion, and sedimentation are responsible for making meteoric gold accessible to humans. The first gold discoveries in the United States were along the Appalachian Mountains, where placer deposits have accumulated. A placer deposit is where the settling of eroded, broken, crushed, moved, and deposited minerals occur. When the final resting place for these tiny particles of gold is in water, it is called alluvial gold. Here, miners use panning, sluicing, or more aggressive dredging to separate gold particles from the other minerals that have settled. 

Only some gold has been released through erosion. The rest is in the form of veins in bedrock or embedded in iron-rich igneous rocks in microscopic forms, as in the case in Nevada. To get this gold, one must use a process called hard-rock mining. 

From meteorites to the ring on your finger, this series will continue to explore the story of where your gold comes from. Stay tuned next month to learn more in the next story in our blog series.